Thermodynamics' zeroth law in a nonextensive scenario

We show how to reconcile Tsallis' thermostatistics with thermodynamics' zer oth law, by recourse to the so-called optimal Lagrange multipliers formalis m, The central concept is that of not identifying in the usual fashion the inverse temperature with the Lagrange multiplier associated to the internal energy. Our analysis provides one with compatibility conditions between th e additivity of the internal energy and the pseudo-additivity of the genera lized entropy, With regards to the first law of thermodynamics, a generaliz ation of Clausius' equation is advanced, (C) 2001 Elsevier Science B.V. All rights reserved.